JPH0650889A - Near-infrared analytical apparatus - Google Patents

Abstract

PURPOSE:To achieve a high-speed measurement by a near-infrared analytical apparatus, to increase the measuring accuracy of the apparatus and to increase the stability of the apparatus. CONSTITUTION:An analytical system wherein a tungsten halogen light source 1, a diaphragm 2 which narrows a measuring light flux from the light source, a condensing optical system 3 which condenses the measuring light flux and which guides it to a measuring part and an integrating sphere 6 for the measuring part on which a sample is placed is arranged on a base 11. An entrance slit 15 for a spectroscope part 40 is arranged on the bottom face of the integrating sphere 6 for the measuring part. A diffraction grating 12 which diffracts and disperses a light flux incident from the entrance slit 15, an array-shaped detector 14 and a reflecting mirror 13 which bends the light flux diffracted and dispersed by the diffraction grating 12 and which forms the image of the light flux, in a dispersed manner, on the face of the array- shaped detector 14 are installed in the spectroscope part 40. When signals from the array-shaped detector 14 are accessed sequentially, a wavelength can be scanned electrically, the high accuracy of the wavelength can be maintained for a long time, and a measurement can be performed at high speed. When the measurement is repeated and its data are integrated, a measuring noise is reduced and the measuring accuracy of the title apparatus can be enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a near-infrared analyzer for quantitatively and / or qualitatively analyzing a sample by measuring optical characteristics of transmitted light and reflected light of the sample in the near infrared region. . The near-infrared analyzer is used as an apparatus for measuring the spectroscopic characteristics of agricultural products, processed foods, chemical substances, drugs, etc. with respect to light.

[0002]

2. Description of the Related Art A near-infrared analyzer was originally developed for analysis of protein and moisture in wheat,
Since then, measurement targets have expanded to fields such as processed foods, alcoholic beverages, chemical products, and chemicals. In the analysis method using the near-infrared analyzer, generally, the sample to be measured is not chemically pretreated, that is, the sample is attached to the measuring device in a non-destructive state for measurement. In an example of the quantitative analysis method, an absorption spectrum or a reflection spectrum is measured mainly over a certain wavelength range in the near infrared wavelength range or at a plurality of wavelength points in at least the near infrared wavelength range, and multiple regression analysis is performed on the data. Then, the amounts of a plurality of components in the unknown sample are simultaneously quantified based on the calibration curve data prepared in advance from a sample of known components by the same method.

The apparatus used for such a purpose mainly has an analysis purpose in which the same type of measurement is repeated many times every day, such as selection of agricultural products and quality control of processed foods, and the measurement results are Since it has important meaning in quality control and price setting of the sample to be measured, the measurement should be quick, and the accuracy should be comparable to the conventional chemical analysis method, and short-term and long-term It is required to have high stability.

In the apparatus conventionally used for satisfying the above purpose and required performance, considering the structure of the spectroscope section as a reference, the method of scanning the wavelength of the measuring light and the method of measuring with a fixed wavelength are used. And have been adopted. The latter method using a fixed wavelength is a method in which a plurality of narrow-band bandpass filters are prepared, they are switched and inserted in the optical path, and the absorbance at a plurality of wavelengths is measured. This type of device has the advantages of simple structure and low cost, but has the drawback that the measurement wavelength cannot be arbitrarily selected and the measurable sample is limited by the device.

On the other hand, the former wavelength scanning system is provided with a diffraction grating spectroscope and rotates or oscillates the diffraction grating to scan the wavelength of the measurement light emitted from the spectroscope exit slit. According to the device having this configuration, it is possible to freely select the measurement wavelength, and the application field of the device is widened.
It can be used for a wide range of purposes including research purposes.
In order to ensure the above-mentioned required performance, that is, high-speed and high-accuracy measurement, short-term and long-term stability, by a near-infrared analyzer using a diffraction grating spectrometer, design the optical system including the spectrometer bright. It is necessary to speed up the scanning of the diffraction grating with high accuracy and to reduce or compensate for temperature changes and vibrations of various parts of the device. The following devices are known as devices developed to meet such requirements. A method of swinging the diffraction grating by a special cam (for example, US Pat. No. 4,285,596), a method of harmonically vibrating the diffraction grating by a combination of a return spring, detection of a counter electromotive force, and a controlled DC motor (US Pat.
540282), a method of detecting and controlling the rotation angle of a DC motor by a potentiometer (US Pat. No. 4,665,645).
No. 22), a method of oscillating the diffraction grating by controlling the rotation of the motor at a constant speed by the combination of the DC motor and the optical encoder (EPO378108), and further to the conventional visible ultraviolet spectrophotometer or infrared spectrophotometer. As used, there is a method in which the rotation of a motor is converted into a linear motion by a feed screw, and this is converted into the rotation of a diffraction grating by a sine bar.

[0006]

A conventional near-infrared analyzer, particularly an analyzer using a diffraction grating spectroscope, which performs wavelength scanning by rotating or swinging a diffraction grating, has the following problems. There is. Each of the above-mentioned conventional devices mechanically scans the diffraction grating, and therefore requires a complicated power transmission mechanism such as a cam, and its rotation speed is considerably high due to the demand for shortening the measurement time. Therefore, there is a problem in long-term mechanical reliability and accuracy maintenance.

Further, in the method of combining the DC motor and the encoder, since the parts which are vulnerable to vibrations and shocks such as the high precision encoder are used, the noise and the temperature change are remarkable like the agricultural product measurement. There is a problem with short-term reliability when measuring outdoors. Further, both the motor and the encoder are mechanical parts that rotate in rotation, and the bearings and the like thereof have a mechanical life, and there is also the problem of deterioration of measurement accuracy due to wear and deterioration due to long-term use. An object of the present invention is to provide a near-infrared analyzer capable of high-speed measurement, capable of enhancing measurement accuracy, and stable in the short term and the long term.

[0008]

The present invention is directed to a light source that emits continuous spectrum light in the near infrared region, a condensing optical system that condenses the light generated from the light source and introduces the light into a measuring unit, which will be described later. A measuring unit for irradiating a sample with light from a light source introduced through an optical optical system, a spectroscope unit for providing light after passing through the measuring unit with a diffraction grating to form a dispersed image on a substantially flat surface, and the spectroscopic unit. An array detector having sensitivity in the near-infrared region, which is arranged on the image plane of the container portion, and a signal processing circuit which processes an output signal of the detector are provided.

[0009]

The spectroscope section is provided with a diffraction grating so that the measurement wavelength can be arbitrarily selected, and since it has no mechanical driving section, it has excellent short-term and long-term reliability. Since the array-shaped detector is electrically scanned to obtain the measurement data for each wavelength, the scanning speed can be increased, and therefore, the accuracy can be improved by the integration effect by the repeated scanning.

[0010]

Embodiment An embodiment will be described with reference to FIGS. 1 is a plan view, and FIG. 2 is a sectional view taken along the line XX 'in FIG. Reference numeral 1 denotes a light source, which includes an elliptical reflecting mirror 1a and a light source lamp 1b, and the light source lamp 1b is the first elliptic reflecting mirror 1a.
It is located at the focal point. The light source lamp 1b is a light source that emits continuous spectrum light in at least a near infrared wavelength range, more specifically, a wavelength range of about 1000 to 2600 nm,
Further, considering the expandability of the device, it is desirable that the device also emits light having a wavelength in the visible range. A tungsten halogen lamp is used as an example of such a light source lamp 1b. The light source lamp 1b is assembled so that the light emitting point, that is, the position of the filament, overlaps the first focal point of the ellipsoidal mirror 1a, and the filament image is formed at the second focal point of the ellipsoidal mirror 1a. An optical diaphragm 2 is installed at the second focal point of the ellipsoidal mirror 1a, and an aperture having a predetermined size is positioned at the position of the filament image to limit the size of the light flux in the optical system thereafter. Also,
In some cases, in order to avoid an undesired state in which the filament image of the light source is imaged on the sample surface or the diffraction grating surface and the illuminance distribution becomes uneven, the ellipsoidal mirror 1a is slightly displaced from the second focus. It is also possible to install the optical diaphragm 2 at the position and use the blurred filament image as the second light source.

A condensing optical system 3 is installed in order to condense and introduce the light flux that has passed through the optical diaphragm 2 into the measuring section.
The condensing optical system 3 includes two plano-convex lenses.
Since the measurement wavelength range is about 1000 to 2600 nm, if a lens is used, there is a loss of light due to absorption by the lens itself, so anhydrous silica glass is used as the lens material. The condensing optical system 3 is not limited to the configuration of the embodiment, and a spherical or aspherical reflecting mirror may be used, for example, in which case the problem of light loss due to absorption of the optical element itself occurs. Absent.

An integrating sphere 6 is installed in the measuring section, and a sample holder 7 is provided in an outlet window facing the inlet window of the integrating sphere 6.
The sample 17 held by is installed. The measurement light 18 condensed by the condensing optical system 3 is introduced from the entrance window of the integrating sphere 6 and irradiated on the sample 17. Measuring light 18 by the condensing optical system 3
Is adjusted so as to form an image of the optical diaphragm 2 at approximately the entrance window position of the integrating sphere 6. This is to prevent the sample 2 from being heated by the formation of an image of the diaphragm 2 or the like on the surface of the sample 17 installed at the exit window of the integrating sphere, thereby lowering the accuracy of the measured value. . However, by providing a means such as inserting a filter that cuts the heat rays outside the measurement range into the light source part, the temperature rises so that the measurement is affected even if the sample is irradiated by the light flux imaged on the sample surface. If there is not, it is possible to form an image of the diaphragm 2 or the like on the sample surface so that the measured range becomes clear. The inner surface of the integrating sphere 6 is close to a perfect diffusive reflecting surface, has a high reflectance in the measurement wavelength range, and has a low wavelength dependence,
Specifically, it is a hollow sphere having a light flux entrance / exit window made of, for example, barium sulfate coating, gold plating, fluorine resin, ceramics, or the like. The diffuse reflection light from the sample can be efficiently grasped by the integrating sphere 6 having such a configuration.

The measuring light 1 is located on the measuring light incident side of the integrating sphere 7.
The dark feather 4 which connects 8 is installed. The dark blade 4 has, for example, a fan shape as shown in FIG. 3, and is controlled by a motor 5 so as to swing or rotate in a direction indicated by an arrow in FIG. The light is blocked so that the dark resistance or the dark current of the detector can be corrected while the light is blocked. An optical system including a light source 1, a diaphragm 2, a condensing optical system 3, a dark blade 4, and an integrating sphere 6 is arranged on a base 11.

The sample 17 placed on the integrating sphere is used in various states for the purpose of measuring the device. In the embodiment, for example, the sample holder 7 is cup-shaped and has a translucent lid, and the sample holder 7 can be filled with a powder sample such as wheat flour for measurement. The sample holder 7 is pressed and fixed to the exit window of the integrating sphere 6 by a pressing means (not shown).
The sample is replaced by the measuring unit lid 1 which constitutes a part of the device cover 9.
By opening and closing 0. When the sample is a solid such as vegetables or fruits, the sample holder 7 may not be used and the sample may be directly brought into contact with and fixed to the integrating sphere outlet window.
Further, when performing the transmission measurement of the liquid sample, the liquid sample is put in a container such as a square cell and the measurement light 18 is incident on the integrating sphere 6 at a position B shown by a broken line in FIG. The measurement can be performed by inserting the integrating sphere 6 into the position and closing the exit window of the integrating sphere 6 with a white plate or the like.

The entrance slit 15 of the spectroscope unit 40 is arranged on the bottom surface of the integrating sphere 6. The spectroscope section 40 is the base 1
It is attached below the base 11 at one end.
The spectroscope section 40 is provided with a diffraction grating 12 that diffracts and disperses the light beam incident from the entrance slit 15.
A reflecting mirror 13 is provided in order to bend the dispersed light diffracted by 2 and form a dispersed image on the surface of the array detector 14. The diffraction grating 12 is configured to allow a part of the inner wall surface of the integrating sphere to be seen from the slit 15. Since the light flux entering the spectroscope unit 40 from the entrance slit 15 is limited by the field of view of the spectroscope itself, a light flux unrelated to measurement such as white light before sample irradiation does not enter the spectroscope. The diffraction grating 12 is a concave diffraction grating in the embodiment, and has a groove interval,
The function of correcting aberration is provided by adjusting the groove shape and the like. Such a diffraction grating can be manufactured by machining with a ruling engine or by a holographic method. The number of grooves in the diffraction grating, the blaze wavelength, etc. are determined by the performance specifications required for the device, such as the measurement wavelength range. The reflecting mirror 13 is a plane mirror for bending the diffracted light from the diffraction grating 12 and introducing the diffracted light into the detector 14. Although the reflecting mirror 13 does not itself contribute to image formation,
This is an effective means when it is difficult to directly guide the diffracted light from the diffraction grating 12 to the detector 14 due to the size of the detector 14, and it is effective in reducing the size of the spectroscope unit 40.

On the detector 14, the diffracted light forms an image in a substantially planar manner. In the case of the embodiment, the imaging magnification of the spectroscope is approximately 1:
If it is configured so as to be 1, the substantially equal-sized image of the entrance slit 15 is formed on the detector surface. On the other hand, the detector 14 is an array detector composed of elements having sufficient sensitivity in the near infrared measurement wavelength range. In the embodiment, PbS elements are arranged in an array on a single substrate. For example, InGaA is not limited to this.
It may be composed of a semiconductor element such as s, InGaAsP or PtSi. Assuming that the image formed on the surface of the detector as in the embodiment is a substantially equal image of the entrance slit 15, the size of the entrance slit 15 is determined by the size of one element of the arrayed detector 14, Even if the slit 15 is widened further than this, the light beam extends beyond the detector 14 and does not contribute to an increase in the amount of received light.

An example of the PbS array detector 14 used for the detector 14 of the embodiment is shown in FIG. In the array detector 14, for example, a PbS element 20 is adhered in an array shape on a quartz glass substrate 21 through a pattern mask, and a quartz cover glass 22 is further adhered on the PbS element 20 to connect wirings from each PbS element. The connector board 23 for this purpose is provided on the back surface. Such a PbS array detector is sold, for example, by Hamamatsu Photonics KK. P
Unlike a silicon photodiode array manufactured by a silicon process, a bS element has a difficulty in building an electronic circuit such as a multiplexer in the element.
Generally, the wiring from each of the elements forming the array must be taken out. Therefore, the substrate 23 for wiring processing and connector arrangement is required, and the signal from the element is taken out through the connector 24 on the substrate 23. For this reason, the size of the entire array detector is not necessarily small, and it may be difficult to incorporate the spectroscopic unit 40 so as to directly receive the diffracted light from the diffraction grating 12 as it is. By using 13, it is possible to solve this problem and increase the degree of freedom in the installation position of the array detector.

The number of elements forming the array is selected and determined depending on the bandwidth, data interval, wavelength range, etc., but for example, the number of elements of about 256 or 512 is suitable for use in near infrared analysis. is there. Assuming that the number of elements is 25
6. If the wavelength range is set to 1100 to 2500 nm, the data collection interval will vary depending on the wavelength, but will average about 5.5 nm / element, which is much finer than the conventional filter switching type device. Is possible, which is sufficient for near infrared analysis. Further, the data interval can be easily reduced by increasing the number of elements. On the other hand, the spectral band width of each element of the diffracted light imaged on the detection surface changes depending on the performance of the diffraction grating itself and the design of the spectroscope. A sufficient bandwidth can be obtained for external analysis.

FIG. 5 shows a schematic configuration of a signal processing system in one embodiment. Each PbS constituting the PbS array detector
The signal of the element 20 is taken out via the connector board 23 and the connector 24. A preamplifier 30 for amplifying the extracted signal and an integrator 3 for integrating the amplified signal for a predetermined time
1 is provided for each element. A multiplexer 32 is provided to sequentially call the integrated signals from the integrators 31 from the respective elements, and an AD converter 38 is provided to convert the called signals into digital signals and take them into the CPU 33. The CPU 33 processes the captured signal as measurement data. It is also possible to reduce noise and improve measurement accuracy by repeating scanning a plurality of times for amplifying and integrating the signal of each element and fetching it into the CPU 33 and integrating the measurement signal in an analog or digital manner.

The CPU 33 sequentially reads the signals from the respective PbS elements 20 to perform data processing for reconstructing the absorption spectrum or the reflection spectrum, controls the dark blade motor control circuit 34 and the light source control circuit 35, and uses the keyboard 37. Is also controlled, and the measurement result is displayed on the CRT screen 36. The measurement data is rarely displayed as a simple spectrum, and it is common to statistically process the measurement data to obtain quantitative or qualitative data of the sample as the final result. Such statistical processing may be performed by the CPU 33, and if the ability is not sufficient, another personal computer or the like can be used.

Next, the operation of the embodiment shown in FIGS. 1 to 5 will be described. Prior to the measurement of the sample, a reference diffuse reflection plate prepared separately is placed in the exit window of the integrating sphere 6,
Data obtained by irradiating the reference diffuse reflection plate with the measurement light is stored as a reference value. The measurement can be performed by comparing the transmission characteristics or reflection characteristics of various samples with a reference value obtained by a reference diffuse reflection plate. In the sample measurement, the sample is held by the sample holder 7 or directly placed at the position of the exit window of the integrating sphere 6. The measuring light from the light source is a condensing optical system 3
The light is focused on the sample 17 and irradiated onto the sample 17. The measurement light reflected from the sample 17 is trapped in the integrating sphere 6 and is multiply reflected by the inner wall surface of the integrating sphere. The reflected light from the sample that has been multiple-reflected by the integrating sphere 6 enters the spectroscope unit 40 through the entrance slit 15 on the bottom surface of the integrating sphere 6, is dispersed by the diffraction grating 12, and passes through the reflecting mirror 13 to form the array detector 14. And is received simultaneously over multiple wavelengths.

FIG. 6 shows the measuring section in the second embodiment. In FIG. 6, the sample 17a is the white measurement light 18
It is illuminated by and is diffusely reflected. The sample 17a is a locally uniform sample that does not depend on the irradiation position. The sample 17a is illuminated with white measurement light and diffusely reflects it. The diffused reflection characteristics of the sample can be measured in the same manner as in the first embodiment by allowing the reflected light to enter the spectroscope section 40 similar to that in the first embodiment from an oblique direction.
In the embodiment of FIG. 6, the integrating sphere 6 required in the first embodiment is used.
Is unnecessary.

FIG. 7 is a diagram showing the measuring section of the third embodiment. In the example of FIG. 7, the sample 17 is arranged not at a position facing the entrance window of the integrating sphere but at a position 90 degrees from the entrance window, and the measurement light 18 irradiates a part of the inner wall of the integrating sphere 6. The positions of the integrating sphere 6 and the sample 17 are set. In this example, the sample 17 is diffused by the light diffusely reflected on the inner surface of the integrating sphere.
Is irradiated. The reflected light in the 0 degree direction of the sample irradiated with the diffused light is guided by the condenser lens 39 to the entrance slit 15 of the spectroscope section and introduced into the spectroscope section, and thereafter, the first and second embodiments described above. It is metered in the same way as. In the embodiment shown in FIG. 7, since the sample is not directly irradiated with strong measuring light, it is possible to prevent a measurement error due to, for example, a temperature rise of the sample.

In the embodiment, a detector in which PbS elements are arranged in an array is used as the detector. For example, the detector is an InGaAs element manufactured by a semiconductor process and the like and a multiplexer is provided on the same substrate as the detector. It is possible to further simplify the configuration of the signal processing system by forming a circuit such as.

[0025]

According to the present invention, the signals from the array detectors placed on the dispersed light image forming plane are sequentially retrieved while the diffraction grating of the spectroscope unit is fixed without mechanical scanning. , It is possible to electrically scan the wavelength, and it is possible to maintain high wavelength accuracy for a long period of time by appropriately performing the initial adjustment. further,
The scanning speed of the wavelength can be significantly increased compared to the case of using the mechanical method.
By repeating the measurement and integrating the data, it is possible to reduce the measurement noise and improve the measurement accuracy, and it is possible to realize an analyzer suitable for near infrared analysis.

[Brief description of drawings]

FIG. 1 is a plan sectional view showing an embodiment.

FIG. 2 is a cross-sectional view taken along line XX ′ in FIG.

FIG. 3 is a front view showing a dark blade in the embodiment.

FIG. 4 is an exploded perspective view showing an array detector according to the same embodiment.

FIG. 5 is a circuit diagram showing a signal processing system in the embodiment.

FIG. 6 is a side sectional view showing a measuring section in the second embodiment.

FIG. 7 is a side sectional view showing a measuring section in a third embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 light source 3 condensing optical system 6 integrating sphere 12 diffraction grating 14 array detector 15 spectroscope entrance slit 17, 17a sample 18 measurement light

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nakamura Kan 1 Nishinokyo Kuwabara-cho, Nakagyo-ku, Kyoto City Kyoto Prefecture Shimadzu Corporation Sanjo Factory

Claims (1)

[Claims] 1. A light source that emits continuous spectrum light in the near-infrared region, a condensing optical system that condenses the light generated from the light source and introduces the light into a measurement unit described later, and the light is introduced through the condensing optical system. A measuring unit that irradiates the sample with light from a light source, a spectroscope unit that includes a diffraction grating and disperses and forms an image of the light after passing through the measuring unit on a substantially flat surface, and a spectroscope unit that is disposed on the imaging surface of the spectroscope unit. A near-infrared analysis device, comprising: an array-shaped detector having sensitivity in the near-infrared region; and a signal processing circuit for processing an output signal of the detector.